1. Field of the Invention
The present invention relates to an air conditioner and a control method of an air conditioner.
2. Description of the Related Art
For an electronic substrate mounted on an outdoor unit of an air conditioner, a guaranteed minimum temperature that guarantees its operation is set, and at a temperature under the guaranteed minimum temperature, an electronic component on the electronic substrate may malfunction and may be broken. As a measure against this problem, it can be considered to use an electronic component having a low guaranteed minimum temperature. However, if an electronic component having a low guaranteed minimum temperature is used, downsizing is hindered or cost increases. It can be considered to attach a heater to the electronic component. However, in this case, downsizing is hindered because of the heater and cost and power consumption increase.
Furthermore, in an outdoor unit of an air conditioner under a low-temperature environment, “stagnation” of a refrigerant may occur while a compressor is stopped because of accumulation of the refrigerant in the compressor. When “stagnation” of the refrigerant occurs, a load at the time of startup of the compressor increases, and thus problems such as breakage of the compressor, breakage of the electronic component due to increase of a starting current, or failure to start the compressor due to system abnormality may occur. As a measure against these problems, it can be considered to install a heater in the compressor to perform appropriate heating or to preheat the compressor by locked energization of an electric motor under a condition in which the electric motor of the compressor is not rotated.
Locked energization is broadly divided into DC locked energization and AC locked energization. In the DC locked energization, heat is generated by a loss of a resistance component of a winding of a compressor electric motor (for example, Japanese Patent Application Laid-open No. H8-226714). In the AC locked energization, heat is generated by a loss of a reactance component of a winding of a compressor electric motor (for example, Japanese Patent Application Laid-open No. H11-159467).
However, according to these conventional techniques, in the DC locked energization, because the resistance component of the winding of the compressor electric motor is used, a large current is required to obtain a sufficient amount of heat generation, the loss is large, and thus power efficiency is poor. On the other hand, in the AC locked energization, because the reactance component of the winding of the compressor electric motor is used, when an AC current of a high frequency is applied, the amount of heat to keep the compressor warm can be obtained with a small current. However, because the degree of temperature increase is lower than the DC locked energization, a long time is required to supply a sufficient amount of heat to keep the compressor warm under an extremely low temperature environment. Therefore, even if the locked energization is used, power consumption increases or a long time is required to reach an intended temperature.
The present invention has been achieved in view of the above problems, and an object of the present invention is to provide an air conditioner for which cost and power consumption are suppressed without increasing the size of the air conditioner, even in a case where stagnation of a refrigerant occurs and the air conditioner is installed in a low temperature environment, in which the temperature falls below a guaranteed minimum temperature of an electronic component.